Radiation systems are used in a variety of applications including treatment of patients. In operation, a radiation source may be moved using a rotating gantry to aim radiation beams at a tumor site from multiple angles. One type of gantry is in the shape of a C-arm, on which the radiation source is mounted in a cantilevered manner and rotated about an axis passing through the tumor site. Another type of gantry is in the shape of a toroid or ring, which has a central opening or bore to allow the patient's body to extend through. The radiation source is mounted on the perimeter of the ring and rotated about an axis passing through the tumor site.
Radiation systems using a C-arm or ring gantry have complementary strengths and weaknesses. A major advantage of C-arm systems is that they allow for implementation of non-coplanar treatments through the use of a combination of different gantry rotation angles, multi-leaf collimator (MLC) adjustments, and patient table maneuvers. These treatments can be either fixed-field or arc-based, conformal or modulated. Disadvantages of C-arm systems are that, due to their open geometry, collision avoidance can be very complicated, cone beam computed tomography (CBCT) scan times are long (on the order of 30 seconds to 1 minute) in part due to regulatory requirements, whole-body treatments are not enabled, and more elaborate room shielding may be required to block radiation not intercepted by the C-arm apparatus itself. Conversely, ring gantry systems support rapid CBCT acquisitions, do not require complicated collision avoidance systems, enable whole body treatments, and are more conducive to self-shielding. However, a major limitation of ring gantry systems is that they do not readily allow for non-coplanar treatments.